1. Field of the Invention
The present invention relates to novel compositions that contain an activator system that comprises a photoactivator, acid generator and chain extender. Methods and articles of manufacture that comprise such compositions are also provided. In a preferred aspect, the compositions are photoimageable.
2. Background
Curable coatings have been employed for wide range of applications including, e.g., as sealers; components of composition wood products; abrasion resistant coatings such as may be used on vinyl flooring or other construction materials; on textiles; coatings on metals such as beverage can finishes, coatings on electronic parts, and the like; coatings on paper products including curable ink coatings; etc. Curing of the coatings can be accomplished by a number of methods, depending on components of the particular coating composition. Treatment of a coating thermally or with activating radiation such as ultraviolet radiation are common known curing techniques.
Photoimageable coatings are one type of curable coatings and are used for transfer of images to a substrate. In use, the composition is applied as a coating layer on a substrate and the applied layer is selectively exposed through a photomask to a source of activating radiation such as ultraviolet light. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. The pattern in the photomask of opaque and transparent areas define a desired image to be transferred to a substrate.
Photoimageable coatings can form negative or positive images. In the case of a negative-acting composition, exposed portions of the coating layer become less developer soluble as a result of a radiation-induced reaction thereby providing differential solubility between exposed and unexposed coating layer portions. In the case of a positive-acting composition, exposed portions of the composition coating layer become more developer soluble as a result of a photo-induced chemical reaction to also provide differential solubility between exposed and unexposed coating layer portions. These differences in solubility allow for the selective removal upon development of unexposed portions of the coating layer in the case of a negative-acting composition, or selective removal of exposed portions in the case of a positive-acting composition, and thus the transfer of an image to the substrate surface. Portions of the substrate surface bared upon development then may be altered as desired such as by etching. The historical background, types and processing of radiation sensitive compositions, including photoresists, is described for example by Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York (1975); and Moreau, Semiconductor Lithography, Principles and Materials, Plenum Press, New York (1988).
A number of materials have been employed as the photoactivatable component in such radiation sensitive compositions. In particular, materials that generate free radicals upon exposure to activating radiation have been employed. The photogenerated free radicals react with one or more other materials of the composition, e.g. to crosslink other composition materials such as an unsaturated monomer or oligomer crosslinker and an acrylate resin. One significant disadvantage of such composition is that the free radical generator is generally oxygen sensitive. As a consequence, special precautions are required to protect the composition from the ambient atmosphere prior to use, adding to manufacturing time and costs.
Another widely used photoactivatable component generates an acid upon exposure to activating radiation. Cationic photoinitiators are commonly used acid generators. The acid produced by the acid generator can induce or promote chemical reactions in a composition coating layer that provides developer solubility differentials between exposed and unexposed regions. For example, the radiation-generated acid can render exposed areas of a composition coating developer soluble by inducing cleavage of certain components of the composition. See, for example, U.S. Patent Nos. 4,968,581; 4,883,740; 4,810,613; and 4,491,628, which describe photogenerated acidic cleavage of certain "blocking" groups pendant from a resin binder, or cleavage of certain blocking groups that comprise a resin binder of positive-acting compositions. In other systems, the radiation-generated acid can render exposed areas of a composition coating effectively developer insoluble by crosslinking of certain composition components. For example, one such negative acting composition highly useful as a photoresist contains 1) a photoactivatable acid generator, 2) a resin binder such as a phenolic resin, and 3) a crosslinker component such as an amine-based material, particularly an a melamine, urea-based material, or benzoguanamine. See, for example, European Patent Applications 0164248 and 0232972. Exposure of a coating layer of the composition to activating radiation results in generation of acid, which in turn catalytically promotes a reaction between the crosslinker and resin binder components to render exposed areas effectively developer insoluble.
While such cationic-based compositions can be highly useful, at least for certain applications they can present notable limitations. Specifically, known cationic photoinitiators generally can be activated by only certain radiation wavelengths. Consequently, to activate a composition at a wavelength to which photoinitiator is by itself not sensitive, either the composition is simply not used for that application, or an additional "sensitizer" material is added to the composition to enable activation of the photoactive component. Use of such a sensitizer is often undesired as it adds an additional component to the composition and can complicate production and use of the radiation sensitive composition.
It thus would be desirable to have a new activation system that would be suitable for use in coating compositions, including photoresists and other photoimageable compositions. It would be particularly desirable to have new photoimageable compositions, including new positive-acting and negative-acting photoresist compositions, that could be activated at a wide range of exposure wavelengths without use of an additional sensitizer material.